linux-kernel - Re: [PATCH v3 1/8] lib: prepare zstd for preboot environment

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Date:   Thu, 26 Mar 2020 18:50:43 +0000
From:   Nick Terrell <terrelln@...com>
To:     Petr Malat <oss@...at.biz>
CC:     Nick Terrell <nickrterrell@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chris Mason <clm@...com>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        Adam Borowski <kilobyte@...band.pl>,
        Patrick Williams <patrickw3@...com>,
        Michael van der Westhuizen <rmikey@...com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        Patrick Williams <patrick@...cx.xyz>
Subject: Re: [PATCH v3 1/8] lib: prepare zstd for preboot environment



> On Mar 26, 2020, at 8:40 AM, Petr Malat <oss@...at.biz> wrote:
> 
> Hi Nick,
> I finally got some time to review your patch, here are my comments:
> 
> On Wed, Mar 25, 2020 at 12:58:42PM -0700, Nick Terrell wrote:
>> * Don't export symbols if ZSTD_PREBOOT is defined.
> I'm not sure if this is needed. When I worked on my patch, I have found that
> all exporting and modinfo macros generate symbols in modinfo and discard.ksym
> sections, which are then dropped by the vmlinux linker script, thus one
> will get the same binary independently if he puts this change in or not.
> 
> I'm not sure if this is intentional as there is also __DISABLE_EXPORTS define,
> which should be used by a decompressor (according to comments in export.h).

This is not my area of expertise, I’m a zstd developer not a kernel developer.
For that reason I wanted to pick the safe route of disabling the exports explicitly,
since that is what the other decompressors do, so I know it works.

If you’re confident that it isn’t necessary, I can drop the modification. But, I do
prefer this approach, because there is no magic involved. I can see what is
happening clearly just by looking at the decompress_unzstd.c code.

Thanks for the review,
Nick